Outlook Explains | Why Air India's Phuket-Delhi Flight Suddenly Dropped 300 Feet Mid-Air

Air India flight AI2379, operating from Phuket to Delhi, encountered severe turbulence during its journey on August 4, leaving at least 17 passengers and crew members injured after the aircraft experienced a sudden change in altitude. The Airbus A320neo landed safely at Delhi’s Indira Gandhi International Airport, where the injured were taken for medical attention.

Air India described the episode as a brief turbulence-related event that caused a “momentary change in altitude”. Authorities are investigating the incident, including the aircraft’s flight data and cockpit voice recordings.

What happened on AI2379?

AI2379 was flying from Phuket to Delhi when it encountered severe turbulence while cruising at an altitude of above 36,000 feet. Reports said the aircraft suddenly dropped around 300 feet, throwing some passengers and crew members around the cabin. Several people were injured, with some requiring medical treatment after the aircraft landed in Delhi.

Air India said the aircraft subsequently continued its journey and landed safely. The airline characterised the incident as a brief turbulence-related occurrence rather than an uncontrolled loss of the aircraft.

The exact sequence of events, however, is yet to be established. Authorities have begun examining the incident, with the aircraft's Flight Data Recorder and Cockpit Voice Recorder expected to help determine what happened in the cockpit and how the aircraft responded to the atmospheric disturbance.

The distinction is important, a reported altitude drop does not, by itself, mean that an aircraft was close to crashing. Commercial aircraft are designed to withstand substantial atmospheric disturbances, while pilots are trained to manage turbulence and associated changes in altitude and airspeed.

The more pertinent question might be about any technical problems that might have caused the incident. A DGCA official quoted by The New Indian Express attributed the fault to a “suspected transient technical fault.”

What causes severe turbulence?

Turbulence is essentially irregular movement of air. It can be produced by several atmospheric phenomena, including thunderstorms, jet streams, wind shear, mountain waves, weather fronts and changes in atmospheric pressure. It can also occur when the sky appears clear, making some forms of turbulence particularly difficult to anticipate.

Thunderstorms are particularly important because powerful updrafts and downdrafts can develop inside and around them. Rain-cooled air can descend rapidly while warm air rises, producing strong vertical currents. Wind shear — a rapid change in wind speed or direction over a short distance — can add to the instability.

Aviation authorities classify turbulence according to its effects on an aircraft. Severe turbulence is associated with large, abrupt changes in altitude or attitude and substantial variations in indicated airspeed. Occupants can be thrown violently against their restraints and unsecured objects can become airborne.

This is why turbulence can be dangerous to people inside an otherwise airworthy aircraft. The greatest immediate risk is often not the aircraft breaking apart, but passengers or crew being thrown into the cabin if they are not secured.

Why is monsoon flying more challenging?

The monsoon does not automatically make flying unsafe, but it can create weather conditions that make flight operations more complicated.

Moist, unstable air associated with monsoon weather can contribute to the formation of thunderstorms and heavy rain. These systems can contain strong updrafts, downdrafts and wind shear — all conditions associated with turbulence. Thunderstorms can also develop or intensify relatively quickly, making the atmosphere more dynamic than it may appear from the ground.

For pilots, the challenge is therefore not simply “rain”. It is identifying and avoiding areas of potentially hazardous convection and adjusting the flight path when necessary.

Aircraft crews receive weather forecasts and warnings before and during flights. They can also use reports from other aircraft to identify turbulence along a route. Aviation weather systems provide information about areas where moderate, severe or extreme turbulence may occur.

Is a 300-foot drop unusual?

A sudden 300-foot altitude change can certainly be alarming, but the number alone does not tell us how dangerous an encounter was.

Turbulence can cause temporary altitude deviations as an aircraft moves through rapidly changing air currents. Aviation procedures specifically recognise turbulence-related altitude deviations, FAA guidance, for example, requires pilots to notify air traffic control when severe turbulence or mountain-wave activity produces deviations of approximately 200 feet or more in certain high-altitude operations.

That does not mean a 300-foot deviation is routine or insignificant. Severe turbulence is capable of producing large and abrupt changes in altitude, attitude and airspeed. But the aircraft's altitude at the time, the duration and rate of the change, airspeed, aircraft attitude, autopilot response and surrounding weather all matter when assessing the seriousness of an event.

Therefore, the reported 300-foot figure should not be interpreted on its own as evidence that the aircraft was in danger of crashing.

Can pilots predict turbulence?

Pilots can forecast and avoid areas of turbulence, but they cannot reliably predict every turbulent patch in advance.

Before and during a flight, crews can use weather forecasts, turbulence guidance, SIGMETs and reports from other aircraft. Pilots can then alter altitude or request a different route when conditions warrant it.

The problem is that turbulence can be highly localised and can change quickly. Clear-air turbulence is especially difficult because it can occur without visible clouds or obvious weather systems. The International Civil Aviation Organization notes that clear-air turbulence is particularly difficult to predict because of its dynamic nature.

Modern forecasting is nevertheless improving. Aviation weather agencies use increasingly sophisticated numerical models and turbulence guidance products to identify areas of potential turbulence. But these systems provide probabilities and forecasts rather than a guarantee that a particular aircraft will encounter — or avoid — a specific pocket of disturbed air.

For passengers, the most effective protection remains simple: keep the seat belt fastened whenever seated, even when the seat-belt sign is off. The Federal Aviation Administration warns that turbulence can occur unexpectedly and that passengers who are not restrained can be thrown from their seats.

The AI2379 incident illustrates the central difficulty of turbulence: an aircraft can be flying normally one moment and encounter a sudden, powerful disturbance the next. The aircraft's safe landing, along with the forthcoming investigation into the flight data and weather conditions, will be crucial to understanding exactly what happened.